# Overview

URL: /docs/middleware/overview/
Section: middleware
Tags: middleware, protocol, pipeline

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No Base Class Chirp middleware uses a Protocol, not inheritance. A middleware is anything that matches this shape: async def my_middleware(request: Request, next: Next) -> Response: # Before the handler response = await next(request) # After the handler return response That is the entire contract. A function that takes a Request and a Next callable, returns a Response. The Pipeline Middleware forms a pipeline. Each middleware wraps the next: Request → Middleware A → Middleware B → Route Handler → Response ↩ Middleware B ↩ Middleware A → Client Middleware registered first runs first on the way in and last on the way out. Registration app.add_middleware(timing_middleware) app.add_middleware(cors_middleware) app.add_middleware(auth_middleware) Order matters. In this example, timing_middleware wraps everything -- it sees the total time including CORS and auth processing. The Next Callable Next is a callable that invokes the rest of the pipeline: from chirp import Next async def my_middleware(request: Request, next: Next) -> Response: # Runs before the handler print(f"Incoming: {request.method} {request.path}") # Call the next middleware (or the handler) response = await next(request) # Runs after the handler print(f"Response: {response.status}") return response You can: Modify the request before passing it to next Short-circuit by returning a response without calling next Modify the response after next returns Catch exceptions from next Short-Circuiting Return early without calling next to block the request: async def auth_guard(request: Request, next: Next) -> Response: if not request.headers.get("Authorization"): return Response("Unauthorized").with_status(401) return await next(request) Response Types Middleware handles all response types through the AnyResponse union: from chirp import AnyResponse # Response | StreamingResponse | SSEResponse For most middleware, you only need to work with Response. Streaming and SSE responses pass through middleware but their bodies cannot be inspected synchronously. Next Steps Built-in Middleware -- CORS, StaticFiles, Sessions, and more Custom Middleware -- Writing your own middleware Routes -- What middleware wraps

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